1. Field of The Invention
The present invention relates generally to solar energy collecting systems.
2. Background Information
Well known for years, the long-term exposure of a material to solar rays causes significant temperature increases in the material's surface and interior. Captured in a material's surface and interior, this heat can be converted and used as an energy source for heating the material's host facility or structure. In a time of diminishing natural resources and rising energy costs and environmental concerns, actual use of solar energy, a virtually inexhaustible resource, through collecting or conversion systems promises an economical, efficient, limitless and environmentally safe energy alternative.
Initially, in an attempt to capture such heat energy from solar rays, collecting systems employed large flat surface materials conducive to the absorption and storage of heat. For unobstructed exposure to solar rays, these surface materials were typically positioned and secured on top of buildings or facilities where the captured heat could be used immediately or stored for future use.
These planar energy absorbing units however create structural loading problems. The weight of each unit proves significant, severely overloading the bracing and support systems of most existing structures. Not originally designed for this excess dead load, the structure typically requires additional reinforcing and major renovations.
Situated on top of the existing structure, these relatively complex systems require a high level of maintenance. Exposed to exterior elements and foul weather often causes damage and malfunction to these systems. Lightning, hail, heavy rains, and wind storms all prove treacherous to these roof mounted systems. Additionally, the relatively complex design of such a system, including its interaction and quantity of heat transfer and storage components, as well as its required structural support network, compel a high level of attention and maintenance.
Although these flat energy absorbing surfaces provide an enormous area for the absorption of solar rays, solar heat does not concentrate on any one given area. This lack of convergence subsequently leads to a high rate of heat loss in the transfer of heat back to the atmosphere and lower circulating fluid temperatures This loss of heat prohibits the production of sufficient energy for economical operation of an air conditioning absorption heating system.
Improvements within the solar energy field introduced the reflection of solar rays onto smaller surfaces, intensely concentrating and focusing the solar rays for more efficient heating. The parabola, when used as the reflective surface, directs reflected rays through one point or focal zone. If positioned correctly in relation to the sun, all rays may pass through a predetermined point or linear zone within the inner area of the parabolic reflective surface.
Responding to these solar energy discoveries and improvements, the market introduced various stationary parabolic reflective troughs which, supported from below, typically mount to the outer surface of a structure's roof. Solar rays reflect off the surface of the entire length of the parabolic trough, reflecting onto a hated fluid-filled conduit which lies along the trough's focal point. The fluid flowing through this conduit is then available for immediate use or storage.
Although this stationary parabolic reflective trough system operates efficiently and effectively when the sun's position causes solar rays to reflect off the trough precisely onto the conduit, constant movement of the sun prohibits continuous maximum reflection. Without maximum reflection and heating, this trough system is unable to provide sufficient temperatures for economic operation of an air conditioning absorption and heating system unit. This inability subsequently places ulterior cooling demands on the structure, requiring use of the reflective system in combination with a standard air conditioning unit. This requirement then proceeds to diminish and erase any monetary advantages predicted for utilization of a reflective trough system.
In addition to creating structural loading problems similar to those created flat energy absorbing panels these stationary parabolic troughs usually demand an even more extensive support system. In addition to its standard elements, the structure must support one or more storage tanks used for the accumulation of heat produced during periods with low energy needs. These storage tanks are required for these systems since production of energy continues through intervals with no energy demands. The tanks, which must sufficiently hold the excess energy produced in the heat absorbing fluid are normally heavy as well as large. This extra weight may require additional support and bracing over and above that required for energy absorbing panels.
The sun's movement, causing continuous change in the area of maximum solar ray concentration, motivated the design of a rotatable parabolic trough, allowing for adjustment in the trough's angle toward the sun. These rotatable troughs, however, were bulky, heavy, and expensive, causing extended loads to the host structure's roof, an unwavering requirement for bottom bracing, support, and mounting, and a monetarily unrealistic energy alternative.
Although the rotatable trough poses structural loading problems similar to the reflective plates and the stationary trough, its bottom bracing, support, and mounting requirements present additional efficiency concerns. Spanning the length of the trough, the fluid-filled conduit typically bows or bends slightly under its own weight. This bowing or bending subsequently causes the conduit to fall outside the parabolic trough's focal zone, preventing reflected solar rays from striking the conduit with maximum efficiency. Conduits operating with stationary reflective troughs, also supported and braced from below, exhibit the same tendency but fail to cause the same level of concern because of the lower efficiency demands and expectations.
In order for the user to recover costs, including the costs for materials, installation, structural bracing, and existing energy system adaptation, the solar collecting rotatable trough must exhibit continuous maximum reflective and collection capabilities. Without this capability, potential users not only face the chore of renovating the intended host structure and adapting the existing energy system, but additionally face the likely possibility that purchase and operation of the solar collecting system will only result in continual monetary loss.
U.S. Pat. No. 4,611,575 teaches a parabolic trough reflector centered around an elongated receiver, the reflected rays concentrating on the receiver. Supported and braced from below, the invention provides an axis about which rotation of the trough may occur. The invention, however, does not teach a method or means for providing continuous solar ray concentration. Additionally, support and bracing from below prevents maximum reflective and collection capabilities.
U S. Pat. No. 4,325,360 teaches a parabolic reflective trough with an absorber pipe along the center of the reflective trough. This absorber pipe acts as support and as an axis for the concrete trough. Sealing of the absorber pipe to the each end of the stationary trough, however, prohibits rotation. As typical with most earlier solar collecting system designs, the cost of the materials alone is prohibitive when considering the system as an energy alternative.
In an effort to utilize the slightly less expensive stationary trough, U.S. Pat. No. 4,396,008 teaches the use of several connecting troughs positioned at different angles. Acting as a sub-collector designed to collect heat during two associated sub-periods of the day, each trough has a primary and secondary heating tube connected in series. Although more efficient than a single stationary trough, such a bulky system still requires support and bracing from below, decreasing the system's maximum reflection capabilities. In addition, the multitude of required materials still leads to a costly and complex collection system.